Cam and method of generating same



F. B. BURT CAM AND METHOD OF GENERATING SAME Feb. 1, 1966 5 Sheets-Sheet1 Filed July 6, 1962 INVENTOR. FARLOW B BURT.

Mys /214i ATTORNEY.

Feb. 1, 1966 F. a. BURT CAM AND METHOD OF GENERATING SAME 5 Sheets-Sheet2 Filed July 6, 1962 INVENTOR. FARLOW B. BURT,

Rim/1M A TTORNEY.

Feb. 1, 1966 F. B. BURT 3,

CAM AND METHOD OF GENERATING SAME Filed July 6, 1962 5 Sheets-Sheet 5INVENTOR.

FARLOW B. BURT.

aid/4M A T ORA Y Feb. 1, 1966 F. B. BURT 3,232,237

CAM AND METHOD OF GENERATING SAME Filed July 6, 1962 5 Sheets-Sheet 4.

A (QO-y;

I R W 24 9- 45 O r 5 l a, I fi' F Cos. X

INVENTOR MAM A TTOR NEY.

FARLOW B. BURT.

Feb. 1, 1966 F. B. BURT CAM AND METHOD OF GENERATING SAME Filed July 6,1962 5 Sheets-Sheet 5 INVENTOR.

FARLOW B. BURT.

A TTOR NE Y,

3,232,237 CAM AND METHUD F GENERATING SAME Farlow B. Burt, Winter Park,Fla, assignor to The Bendix Corporation, South Bend, Ind, a corporationof Delaware Filed an 6, 1962, Ser. No. 208,137 2 Claims. or 103-136) Thepresent application is a continuation-in-part of my copendingapplication Serial No. 18,113, filed March 28, 1960, now abandoned,which in turn is a division of my then copending application Serial No.635,747 filed January 23, 1957, now Patent No. 2,958,264, issuedNovemher 1, 1960.

The present invention relates to positive displacement types ofhydromechanical devices, such as pumps and motors of the sliding vanetype; and more particularly to the cooperating camming surface on whichthe vanes slide; and further to a unique method of making such a part.

An object of the present invention is the provision of a new andimproved cam configuration for a hydromechanical device and which camhas a plurality of lobes and valleys positioned radially about an axisof rotation with the tips of the lobes being uniformly machined toprovide cylindrical surfaces of fixed radius from the axis ofrotationthe lobes and valleys being preferably formed by a continuousrepeating sinusoidal configuration, and the cylindrical surfaces havinga length of from two to five degrees.

Another object of the invention is the Provision of a new and improvedmethod of generating the preferred cam surface mentioned above by meansof apparatus in which the rotatable cutting element is positionedradially with respect to the blank while the center of the cuttingelement and blank are rotated relative to each other to provide acylindrical surface of fixed radius, and thereafter the sinusoidalvalleys are formed by relative radial reciprocating movement between thecutting element and blank until the remaining sections of thecylindrical surface are machined to a predetermined length.

Further objects and advantages will become apparent to those skilled inthe art to which the invention relates from the following description ofthe preferred embodiments described with reference to the accompanyingdrawings forming part of this specification, in which:

FIGURE 1 is a perspective view of apparatus embodying principles of thepresent invention;

FIGURE 2 is a cross-sectional view taken on the line 2-2 of FIGURE 1;

FIGURE 3 is a side view of a cam member finish machined according to thepreferred cam configuration;

FIGURE 4- is a fragmentary side view of a portion of FIGURE 3 betterillustrating a refinement in its contour;

FIGURE 5 is a fragmentary schematic view exaggerating the relationshipbetween the desired cam configuration and cutting element to more fullydepict the principles of the invention;

FlGURE 6 is a fragmentary schematic view exaggerating the relationshipbetween a preferred form of gearing which strangely enough closelyapproximates a desired corrective phase shifting movement in the aboveapparatus; and

FIGURE 7 is a cross sectional view of the vane type ited States Patent 0'ice pump described in Patent 2,985,110 but which includes the cam bodymember of the present invention.

As indicated above, the present invention relates to the part of a vanetype hydromechanical device, be it a pump or a motor, against which thevanes slidingly abut during operation of the device to alternatelyexpand and contract the chambers to which pressure fluid and exhaust iscommunicated. These members against which the vanes slide are commonlycalled cams by the men skilled in the art, and will be hereinafter sodesignated.

There is shown in the drawings apparatus which is specifically designedto machine the cam configuration illustrated in FIGURES 3 and 4 of thedrawings. The cam body member C shown in these views is specificallydesigned for use in sliding vane cam pumps of the type described in theBurt, Sung and Farron application Serial No. 623,144, filed November 19,1956, now Patent No. 2,985,110. In this type of pump, a cylindricalrotor member 8 is mounted within the central opening 10 of the cam, insliding sealing engagement with the radially innermost projecting partsor lobes 12 of the cam. The rotor carries a plurality of vanes 13 whichare biased radially outwardly into engagement with the cam surface 14,to sweep liquid out of the space defined by the valleys, or camdepressions, and the rotor through suitable passages in the rotormember. For a more complete description of the construction andoperation of the pump for which the cam member C is designed, referencemay be had to the above mentioned application.

The specific pump of which cam member C is a part is intended for use inhydraulic power steering systems where substantially pulse free flow isrequired at rotor speeds tan ing from to 4000 r.p.m. and at pressures inexcess of 1000 p.s.i. Numerous problems are involved in designing pumpsfor these conditions. One of these problems is presented by leakage froma high pressure valley to a low pressure valley through the clearancebetween the separating lobe and rotor; and another of these problems ispresented by the dynamic forces of the vanes which tend to'separate themfrom the cam surface. The specific cam contour used in the cam member Cis a sinusoidal one conforming to the equation R=r +e cos at). For amore detailed description of this contour and of the problems ofdesigning pulse free pumps, reference may be had to the above referredto application.

In his work with such pumps, applicant has found that a great reductionin leakage between the cam surface and rotor can be accomplished bymeans of a cylindrical contour in the tip of each lobe without harmfullyaffecting the pulse-free operation of the pump. These cylindricalcontours should be confined to the tips of the lobes; and should extendover an arc of from about 2 to about 5 degrees,

The method and apparatus used by applicant to machine the cam contourpreviously described may best be understood by reference to FIGURE 5 ofthe drawings, wherein the pertinent angles and distances are shownexaggerated to better illustrate the relationship involved. The desiredfinished machined contour is generally indi cated at 15 and theperiphery of a rotatable cutter of predetermined diameter for machiningthe contour is indicated at 16. There is also shown at 18 a line allpoints on which are spaced radially inwardly from the line 15 towardsthe center 0 of the blank a distance R which corresponds to the radiusof the cutter 16. Relatively simple means could be provided for movingthe center of the rotatable cutter along line 18; but were this to bedone, the cutter would not be tangent to the desired contour as seen bythe dot-dash line 20, but would dig out too much metal at some spots andnot enough at others. In order for the above described cam contour to beable to develop substantially pulse free discharge, the cam contour mustbe machined to an accuracy approaching a few ten thousandths of an inch.This can only be obtained by correcting for the above-stated inaccuracyinvolved in the use of a rotatable cutter.

The applicant has theorized that the above errors could be eliminatedwere means to be provided which, it kept in phase relationship with theangle of rotation of the blank, would move the center of the cutteralong a path which is a fixed radical distance from the desired camcontour (i.e. along the line 18); and further has theorized that bysuitably changing the phase relationship between the cutter and theblank, the periphery of the cutter could be made tangent to the desiredcontour at all times. A preferred method of accomplishing these resultswill now be explained with reference to FIGURE 5 of the drawings. Assumefor the time being that a suitable means is used to provide radialmovement between the cutter and the blank, and that a further means isprovided which, when rotated in direct proportion to said first means,moves the center of the cutter along the line 18. Referring to FIGURE 5,the equation for the desired cam contour 15 will be:

r =radius of any point of the cam defined by angle r =mean base circlefor the cam e=maximum variation above and below the base circle n=numberof lobes =the angle between any particular radius and an arbitraryreference line through a center of a valley.

For a cutter of radius R, the radius of curve 18 at any given pointwould be r =r R+e cos 11.

It will be seen that if the cutter is moved in and out on its radius inphase with its position about the cam its center would be at 22 at theangle shown in FIG- URE 5. If the center 22 were moved radially inwardlyto the point 24, the cutter would be tangent to the desired contour atthe point T. Point 24 is the distance S from the center 0; and if thecutter were moved out of phase by the angle 0, it would have a radiusequal to S. Therefore to be tangent, the means moving the cutterradially would have to have moved an angle proportional to ,B when thecutter had moved 5. By means of polar coordinates:

also from the law of sines Constructing a normal from point 24 to theradian en sin nu F=a cos xix R a sin x O=arc sin 5 and x should approach77 times the theoretical of Equation 6.

By cut and try methods applicant was able to establish that, when r=1.25, R=.375, 71:6, e"'.023, R-1 for the gear, and the a value of thetheoretically desired conin the slide plate F and the top plate 48 ofthe frame, respectively, to receive the electric motor E and permitlateral movement thereof relative to the blank C.

The slide F is adapted to be reciprocated generally according to adesired sinusoidal function by an eccentric tour. G and a scotch yokestructure 72 fixed to the slide plate A tabulation of data indicatingthe accuracy with which F. The scotch yoke structure 72 is formed bymeans of the S value provided by the gearing approaches the theoa pairof blocks 74 and 76, adjacent sides of which are retically required Svalue for a perfect contour is as folsuitably recessed to receiveopposite sides of a cylindrical lows; rotor 78. The blocks 74 and 76 areconfined into tight Assuming values of on as indicated, 10 engagementWith opposite sides of the rotor 78 by means RSln (so-r "F Rsin(90 1will? angle "utput S 111 (90) m of gears angle of cos :5 IL-0.23 cos xS1.25-.375 ha S S gears It will be seen that the maximum error is lessthan 2 of a cross-bar 8t and through bolts 82 and 84 which extenthousandths of an inch and is therefore acceptable. 25 tend throughopenings in opposite side spacer members Apparatus embodying the aboveprinciples is. shown in $6 and 88 and are threaded into the end Of theslide plate FTGURES l and 2 of the drawings. The apparatus gen- F. Thespacer members 86 and 8-8 are of a length which orally comprises a frameA on which is journalled a turn- Will provide a tight fit between therotor 73 and the blocks table B for supporting and rotating an annularblank C 74 and 76 to overcome lost motion in the reciprocating to bemachined. The blank is machined by a rotatable 3O strhctilre- Thereciprocating cycle of the cutter D y be cutter D carried by a highspeed electric motor E, which fed radially oiltwtiftiiy ihtQ the blank y1.1163118 0f 11 and in turn is mounted on a slide F adapted to bereciprocated wheel- 90 and rod which is threaded into 21 pp so that thecutter moves in a straight line which passes block 4 and the end ofwhich is adapted to abut he through the center of the blank. The slide Fis moved block The Support block 94 is fixed to Slide F y back and forthby means of the eccentric G which in turn 35 bolts and the end of therod 92 adjacent the and i ot t d by means f gearing H hi h id h wheelhi) is slidably received in an opening 98 in a guide proper lead and lagto and in-andout movement of the I Silltahiy fiXBd t0 the The block 4slide to maintain the cutter tangent to the desired concarrying thehiOtOT E has been preylousty described a tour, as di d b beingadjustably fixed to the slide plate F by means of The turntable B forsupporting and rotating the blank Slotted hoihs 65 bolts 64; and ythreading thfi fOd C comprises a bottom plate 36, the under surface of92 lhwardiy against block 1 the i f y he Which is accurately machined torevolve on a correspondreiatlva to the Shde Plate dltli Indicator 10 iurf 32 i d into the top f f a m. is shown mounted on the block 54 withits sensitive elet l plate 34 of h frame A A f i plate 3 recgssed ment1n engagement w1th the support block 94 such that i i upper f tovreceivethe bottom end f the cutter the depth or cut of the cutter D can bereadily determined. D and to provide chip space is suitably fastened tothe a practlchl h f the bolts 64 may b8 tightened a plate 30; and theblank C is adapted to be clamped there- Point wherein incnon bfitweenthe hlock and Slide to by the bolts 33. The turntable assembly B isrotated Plate F sufficlent to hold the F t cutting engage by means of ashaft (it suitably journalled in the frame ment Wlm the thank and f' SunPerm1t thfi block to A; d th bottom d f haft 49 j Coupled to the bemoved relat1ve to the s l1de by means of the threaded put shaft 42 of agear reducer 44 having an input shaft rod 92 t t further adiusitment ofthe bolts 46 adapted to be driven by dan elgctric motor (not Thecylmdncal rotor 78 is mounted eccentncally on h the end of a shaft 11%by a distance 2 which 1n the The blank 0 n usually be rough machined toan present mstance is equal to 0.023 inch. The shaft 104 internaldiameter approaching the desired distance between 1S Suitably tournanedm the,frame A and dnvfin at opposite lobes of the finished cam. Therotatable cutting t Whlch 1s generfany 51X tunes h the blanjk element Dadapted to machine the finished contour is 15 rotated to Provide a F SIXh and SIX rotatably supported from the electric motor E which in Theshaft m4 duvet from? h 106 turn is supported from the slide structure Fabout to by means P h fl later to h described and the if b described. htop plate 3 f the frame is machined 6O shaft 106 is suitably ournalled1n the frame A and d11ven parallel to the machine surface 32 to providea suitable at a rate six times that of the Shaft 40 by mums of gearssurface on which the slide structure F reciprccates. Oppo- 108 and 11hfixed to t shafts 49 l f site side edges of the slide F are beveled forsliding en- The gear mearis H adapted to pl'owde t gagement With a pairof ways 50 and 52 which in turn by means of which the cutter ht is h i fare bolted to the top plate 43 in a manner assuring that tangent t tdesire/d h Cohtcilf, lltihlhg the p lpi the cutter D Will move radiallyacross the centerline of the p h y described with Thfhrence 9 IGURE oi tturntable B. The electric motor E is supported from the drawingg m HComprises t cyhh-ihlcai slide F by means of blocks 54 and 55, theadjacent ends gears h h hflvlhg a Pitch filametfif Q two inches of whichare suitably recessed to receive opposite sides of whlhh 1S mountefi itsrespective. Shaft eqcwtflcfliiy of the electric motor E; and theelectric motor is clamped y a distance which In the PF 'Q Instance isequal to therebetwfifin by means f h hi b lt 62 Th 0. l061nc-hes. Thegear 112wh1ch 1s fixed to the shaft 106 block 54 is in turn adjustablypositioned upon the slide 0 COIFCSPOIId generally to the left-hand geardehlct'id F by maans of a p lity of bolts 64 which extend through inFIGURE 6; and the gear 114 fixed to the shaft 164 slotted holes 66 inthe block 54 and are threaded into the will correspond to that shown 1nthe rlght-hand slde of the slide plate F. Suitable openings 68 and 70are provided same figure.

In the preferred method of operating the apparatus above described, agear blank C finished to a rough internal diameter will be bolted to theturntable B. The cutter D will be positioned within the opening of theblank C, and the gear 112 will be removed from the shaft 104 so that theslide F will not be reciprocated relative to the blank. The hand wheel90 will be turned to gradually advance the rotating cutter D radiallyinto the blank C until its internal diameter corresponds to the desireddistance between the cylindrical surfaces 116 in opposite lobes of thefinished cam. Once this diameter has been accurately machined the gear112 is inserted upon the shaft 104 and the eccentric means G suitablyrotated to provide reciprocatory movement of slide structure F. Prior tothe time that the slide structure F is reciprocated relative to theblank, the motor E will be moved radially inwardly a sutficient distancesuch that the cutter D will not engage the surfaces of the blank aboutto be machined when the reciprocation of the slide structure is started.Thereafter the rod 92 is threaded inwardly until the reciprocatory cycleis moved outwardly to a point where the cutter D begins to engage theblank during the radially outermost portion of its cycle. Engagement ofthe cutter D during its outermost extremity of radial movement begins toform the valleys in the blank C; and by gradually advancing the rod 92into the support member 94, these valleys will be deepened until allthat remains of the original cylindrical internal surface are thesections which are to be left in the tips of each of the lobes. Thesecylindrical surfaces 116 will be from 2 to 5 degrees in length. It willbe seen that the chordal length of the cylindrical surfaces 116 will begradually reduced as the machining of the cam progresses. Thecylindrical surfaces 116 provide a mark which can readily be seen by theoperator; and when this mark has decreased to approximately 50 or 60thousandths of an inch (which can be judged by eye, by a skilledmachinist) the machining of the cam is complete. By this simpleexpedient the sinusoidal surfaces can be accurately machined to thedesired depth. The apparatus shown in the drawings can be used tomachine external cams as well as internal cams; and by suitablyalternating the eccentric G and gearing H the same principles can beused to form cams having a configuration other than the sinusoidal oneof the cam shown in FIGURE 3.

While the invention has been described in considerable detail, I do notWish to be limited to the particular methods and constructions shown anddescribed, and it is my intention to cover hereby all novel adaptations,modifications and arrangements thereof which come within the practice ofthose skilled in the art to which the invention relates.

Iclaim:

1. The fluid pressure chamber forming cam member of a vane type positivedisplacement fluid handling device comprising: a body member having acontinuous fluid pressure chamber forming slide vane camming surface ofgenerally predetermined width extending about an axis of rotation, saidcamming surface having spaced apart portion which project farthest outof said body member to form lobes and also having valleys between saidlobes which recede into said body member to form said pumping chambers,the outermost surface of each lobe having a cylindrically contouredsection therein with its center of curvature coincident with said axisof rotation and subtending an arc of from 2 to 5 degrees, and each ofsaid cylindrically contoured surface sections being spaced at the sameradial distance from said axis of rotation.

2. The fluid pressure chamber forming cam member of a vane type positivedisplacement fluid handling device comprising: a body member having acontinuous fluid pressure chamber forming slide vane camming surface ofgenerally predetermined width extending about an axis of rotation andconforming generally to the equation r =r +e cos 11 where r =radius ofany point of the cam defined by angle r =mean base circle for the came=maximum variation above and below the base circle n=number of lobes=the angle between any particular radius and an arbitrary reference linethrough a center of a valley the portions of said surface which projectfarthest out of said body member forming lobes, the outer most portionof each lobe having a cylindrically contoured section over an arc offrom 2 to 5 degrees, and the center of curvature of each cylindricallycontoured section coinciding with said axis of rotation.

References Cited by the Examiner UNITED STATES PATENTS 2,174,664 10/1939Korany 12316 2,730,076 1/1956 Hogue 103121 2,845,872 8/1958 Farron et a1'103136 2,992,616 7/1961 Rineer 103-121 FOREIGN PATENTS 1,006,314 1/1952 France.

DONLEY'J. STOCKING, Primary Examiner.

JOSEPH H. BRANSON, JR., KARL I. ALBRECHT,

Examiners.

1. THE FLUID PRESSURE CHAMBER FORMING CAM MEMBER OF A VANE TYPE POSITIVEDISPLACEMENT FLUID HANDLING DEVICE COMPRISING: A BODY MEMBER HAVING ACONTINUOUS FLUID PRESSURE CHAMBER FORMING SLIDE VANE CAMMING SURFACE OFGENERALLY PREDETERMINED WIDTH EXTENDING ABOUT AN AXIS OF ROTATION, SAIDCAMMING SURFACE HAVING SPACED APART PORTION WHICH PROJECT FARTHEST OUTOF SAID BODY MEMBER TO FORM LOBES AND ALSO HAVING VALLEYS BETWEEN SAIDLOSS WHICH RECEDE INTO SAID BODY MEMBER TO FORM SAID PUMPING CHAMBERS,THE OUTERMOST SURFACE OF EACH LOBE HAVING A CYLINDRICALLY CONTOUREDSECTION THEREIN WITH ITS CENTER OF CURVATURE COINCIDENT WITH SAID AXISOF ROTATION AND SUBTENDING AN ARC OF FROM 2 TO 5 DEGREES, AND EACH OFSAID CYLINDRICALLY CONTOURED SURFACE SECTIONS BEING SPACED AT THE SAMERADIAL DISTANCE FROM SAID AXIS OF ROTATION.